The present invention relates generally to a clutch assembly having a hardened metal cone spring which biases a pressure plate into contact with a clutch friction disk, and more particularly, to a clutch assembly having means for protecting adjacent components of the clutch assembly from wear due to contact with the cone spring.
Typically, a clutch assembly is mounted on the flywheel of an internal combustion engine, or other rotary power source and is used to engage and disengage a clutch friction disk. The clutch friction disk is usually connected to a transmission. Engagement and disengagement of the clutch disk facilitates control of the transmission of power from the engine to the transmission. The clutch assembly includes the friction disk positioned adjacent to the flywheel, a clutch cover fixed to the flywheel, a pressure plate coupled to the clutch cover which may be selectively moved to engage and disengage the friction disk, and a biasing means for urging the pressure plate into engagement with the friction disk. A lever member mounted for pivotal movement to the clutch cover contacts the pressure plate and facilitates the movement of the pressure plate in and out of engagement with the friction disk.
The biasing means can be any of a variety of devices. For instance, the lever member may be in the form of a diaphragm spring and may provide all or just a portion of the biasing force. Additional biasing devices, such as a spring or series of springs may also be employed. One such spring is a conically shaped spring disk referred to as a cone spring. The cone spring is generally disposed inside the clutch cover for engagement with the pressure plate. The cone spring has one radial edge supported by the clutch cover and another radial edge pressing the pressure plate against the friction disk and flywheel.
Clutch cover assemblies which utilize cone springs have a variety of problems, such as the following:
1) The edge of the cone spring that abuts against a surface of the clutch cover slides relative to the clutch cover for each clutch engaging and disengaging operation. Since the surface hardness of the clutch cover is usually lower than that of the cone spring, an abutting surface of the clutch cover eventually experiences wear. As the clutch cover is worn, the pressing posture of the cone spring is changed due to the corresponding change in the dimensions of the clutch cover. As a result, the load characteristics of biasing responses of the cone spring are changed since the force imparted by the spring is dependent upon its relative displacement with respect to abutting surfaces.
2) In some clutch cover configurations, the cone spring is maintained in proper radial position by a stepped portion formed in the clutch cover. However, due to the nature of the manufacturing process which may include stamping, rolling or pressing the cover into the desired shape, usually requires the cover to have rounded contours. The rounded contours may not provide the cover with precise dimensions in a mass production process to the degree required for positioning of an element within the cover, such as a cone spring. Therefore, the cone spring cannot be reliably position, whereby the cone spring may, in some cases, radially move out of its proper position. Consequently, the effective load characteristics (the biasing force imparted to the pressure plate) of the cone spring are liable to change.
3) As the friction disk of the clutch assembly wears, the pressure plate moves closer to the flywheel, thus changing the relative positions of the various components of the clutch assembly. As the relative positions change due to clutch disk wear, the portion of the cone spring that engages the pressure plate also moves closer to the flywheel. As the friction disk continues to wear, it is possible for the cone spring to become disengaged or have limited engagement with the pressure plate, later causing an axial clearance between the contacting part of the cone spring and the pressure plate. As a result, the cone spring may develop a backlash or clearance either between the clutch cover and the cone spring or between the cone spring and the pressure plate. The clearance may allow the spring to vibrate, thereby producing abnormal sounds. Such sounds are a source of discomfort for the operator of the machinery equipped with the clutch assembly. In automotive applications, such noises are of extreme discomfort to a driver, and may lead the driver to believe there is a serious problem with his automobile, where no problem exists. Hence, such noises are undesirable.